Mounting piles of municipal biosolids cause headaches for local authorities and resource managers the world over. For those who wish it would all disappear, Scion has developed a technology that could help it do just that.

A hydrothermal deconstruction process being tested in Rotorua offers a new approach to waste management. The environmental technology, known as TERAX^TM , “cooks” sewage biosolids and breaks them down into smaller and simpler organic compounds. Strictly speaking the waste does not disappear, rather it is transformed. The process takes a pile of waste and turns it into useful industrial chemicals, energy or fertiliser products.

Scion and Rotorua District Council (RDC) have constructed a 200 litre/hour pilot plant at Rotorua’s Wastewater Treatment Plant to test the TERAX^TM process as a potential solution to the district’s waste disposal problem. RDC Works Manager Peter Dine says early results from the pilot plant are exciting.

“There is a lot of interest in the process because we can now demonstrate that it actually works. The engineering challenges have been substantial as a whole lot of separate components need to work together, but we can see that it will do what was expected,” he explains.

Since the official opening of the hydrothermal oxidation plant in May 2011, the facility has been expanded to include an anaerobic fermentation plant to allow complete testing of the hydrothermal deconstruction process.

Scion’s General Manager Sustainable Design, Dr Trevor Stuthridge says the anaerobic fermentation plant uses bacterial cultures to pre-treat the organic waste and significantly decrease the volume of material that enters hydrothermal oxidation. The second step in the process uses high pressure and temperature with oxygen to break down the waste material and derive useful compounds from it.

“The greatest advancements have been in the recovery of valuable chemicals from the process, giving us the ability to change the economics of waste disposal by generating value from these biological wastes,” he explains.

To put the nuts and bolts on these science ideas, Scion and RDC worked closely with Longveld Engineering in Hamilton, and Rotorua-based consulting engineers Allan Estcourt Ltd. Trevor says the technical hurdles have been both challenging and interesting as the pilot plant provides a good opportunity for trouble-shooting issues that were not evident at laboratory scale.

Once the plant is fully operational and testing is complete, the next step is to design a commercial plant capable of handling all biosolids from Rotorua’s Wastewater Treatment Plant. That’s where it’s hoped the investment in research and development will pay off.

RDC Chief Executive Peter Guerin says a full-scale plant in Rotorua could initially remove thousands of tonnes of biosolid waste going to landfill per year, if successful.

“Applied to all of Rotorua’s organic wastes, it could ultimately achieve net benefits (cost reduction and value creation) of around $4 million per year for the council and community,” he says.

Research shows the same technology could be used for managing organic wastes from food and industrial processors, such as pulp and paper, agriculture, dairy, meat and fruit processing. With 1.8 million tonnes of organic waste discarded each year in New Zealand, TERAX^TM could transform it into a valuable resource – not magically, but scientifically.